Molecular Orientational Structures with Macroscopic Helix in Antiferroelectric Liquid Crystal Subphases

The helical pitch and the optical rotatory power (ORP) were measured in the subphases of an antiferroelectric liquid crystal. These measurements clearly indicate the existence of a macroscopic helical structure with a pitch of several microns. The selective reflection and ORP in several molecular orientational structures were simulated using the 4×4 matrix method. A comparison between the experimental and simulated results clearly denies the molecular orientational structures based on the clock model, in which the molecules in these subphases form helical structures consisting of several layers. A new, modified structure of the antiferroelectric AF phase was proposed based on ORP in the smectic-C * -AF phase transition and conoscopy studies. This modified structure is consistent with a recent resonant X-ray experiment.